1. Technical Field
This invention relates to optical projection apparatus and, more particularly, to means for generating a light beam of substantially uniform intensity from a multi-element light source initially projecting a beam having a generally Gaussian intensity distribution.
2. Discussion
A laser is a source of high intensity, coherent, monochromatic light that has a number of diverse applications. The laser beam is often generated from a nonplanar array of discrete, mutually spaced light sources such as commonly found in GaAs laser diode arrays. In most applications it is desirable to convert the light from the nonplanar multi-element source into a substantially uniform flat or planar luminous source. U.S. Pat. No. 3,535,507 to Sugino discloses one particularly advantageous method of accomplishing this objective. Briefly, this is accomplished by passing the light through an axially elongated optical duct comprising a body of optical material with totally reflecting side faces, as well as flat entrance and exit faces perpendicular to the optical axis. The body of optical material effectively integrates or homogenizes the discrete nonplanar light sources into a uniform planar beam.
While the above-mentioned patent teaches an advantageous method of generating a planar beam from a plurality of discrete nonplanar sources, the output beam still does not have a uniform distribution of light intensity across its diameter. The technical literature reports several problems that are associated with the nonuniform light intensity distribution of laser beams (see, e.g. P. W. Rhodes et al., "Refractive Optical Systems for Irradiance Redistribution of Collimated Radiation: Their Design and Analysis", Applied Optics, Vol. 19, No. 20, Oct. 15, 1980).
The intensity of a laser beam generally follows a Gaussian distribution, i.e., the beam is more intense along its central optical axis. The high central irradiation is a potential eye hazard when using high powered lasers unless suitable precautions are taken. Still other problems associated with the Gaussian distribution is that it dramatically reduces the optical efficiency in optics such as telescopes with central obscuration.
In an attempt to redistribute the radiation of laser beams, the authors of the above-noted article disclose the use of aspheric refractive elements to normalize the output of the beam to a uniform energy distribution. Some of the drawbacks with this approach include the requirement for at least two additional lenses in the optical system thereby increasing costs, setup time, and other problems that are appreciated by the skilled practitioner.
One particularly advantageous approach to solving this problem is disclosed in U.S. Pat. No. 4,656,562 to Sugino which is assigned to the assignee of the present invention. There, a rod of optically transmitting material with a faceted entrance face is used to integrate or homogenize the light from the discrete, multi-element light sources and effectively invert the cross sectional intensity of the beam entering the entrance face to provide the beam with a more generally uniform intensity as it leaves the exit face. As will appear, the invention of this patent can be even further improved to ensure that there are no localized areas of concentrated energy or "hot spots" as the beam travels through the optical system from the exit face of the rod to the desired output plane.